Free boost modification

[97ChameleonTA]

Thanks to Phil for posting this up! A lot of people can benefit from this information as long as it's done correctly. Too much gap can lead to passing more air through the supercharger during normal driving which will just drive up IAT's.

[PsychoZL1]

I just looked at this today to see how difficult it is and it appears that all you need to do for adjustment is to turn out the set screw rather than moving the whole assembly back.

I'm also curious about any negative effects of doing this as well. Also how cold are we talking in regards to the blade sticking in extreme cold? 10*F? -10*F? More than -10*F? Thoughts on this, just curious if I'm far enough north for this to be an issue?

[GenF-GTS]

Originally Posted by 97ChameleonTA

Thanks to Phil for posting this up! A lot of people can benefit from this information as long as it's done correctly. Too much gap can lead to passing more air through the supercharger during normal driving which will just drive up IAT's.

It vacuum control so it opens 100% as soon as you start the car.
When you are under boost if you have not made the adjustment it is 99.5% closed.

Once you adjust it then it will be 100% closed.

It is similar to a throttle body however vacuum controls it opening and closing so it's either OPEN or CLOSED.

So there is no such thing as more air passing through the charger under normal driving conditions it will be open during non boost driving and air will divert over the charger instead of through it....then when under boost the vacuum will close the blade and it will boost up, if you have made the minor adjustment you will not lose any boost pressure leaking back out of the blade.

[Blueclyde]

Does anybody know if this is an adjustable item? I find it hard to believe that these are all misadjusted from the factory. I'd speculate that there is a reason they are like this. I would be interested to see if there is any mention of adjustment in the GM service manual. It seems likely that this small gap/leak path is there for a reason.

[DrkPhx]

Questions for those reporting a boost increase - Are you datalogging or just viewing the boost gauge? Keep in mind boost is typically higher in colder weather. I would assume you're doing a quick before/after test back to back?

GenF-GTS explained the bypass operation correctly. It's really simple. It's only fully closed at two different times; engine completely off and WOT. Closed = no boost bypass. At idle and part throttle the bypass is open to allow boost bleed off during normal engine operation. It should be adjusted anytime the snout is removed.

This has been an on and off again discussion for the CTS-V owners for a while. For reference here is step 78 from the LPE snout how-to:

Tighten the set screw so that it barely

touches the stop plate on the front cover. After

the initial contact, tighten the set screw 1/8 to

1/4 turn

more to set the bypass valve blade

into position. The set screw should now be

touching the stop plate on the front cover. This

will prevent the bypass valve blade from getting

stuck on the front cover casting. Remove the

bypass actuator set tool.

And a detailed write up how to adjust it from post on that site:

Before adjusting the bypass actuator and arresting screw, it would be wise to understand the design intent and ramifications of incorrect adjustment.

1. On our CTS-V's the bypass actuator is primarily used for unloading the supercharger when boost is not required. I.e., when the engine has vacuum the actuator pulls the plate open so some air can bypass the rotors and feed the engine unhindered (as per Ben's posts).
   • Disconnecting a correctly operating bypass will not assist the engine to create more power (despite what some Ford forums may claim). In fact, it will usually cause an increase in IAT's & will certainly shorten the life of many components.
   
   
2. On the LS9 & LSA platform, the bypass actuator is also used for "bleeding" boost during some of the torque management strategies. If tweaking these strategies is desired, it should be done via tuning the software parameters - not via any mechanical means.
3. An incorrectly adjusted bypass system can cause the bypass throttle-plate to not seat (leak); jam/stick shut (not bypass immediately); pull over-centre & jam/stick open (always bypass); self-destruct (cause the diaphram to tear).

The correct adjustment of the bypass is to have 2.0-2.5mm of preload after the throttle plate is arrested. Therefore, the order of adjustments makes a difference.
I recommend:

1. Back off the arresting/adjustment screw so the lever is well clear.
2. Loosen (not remove) the actuator fasteners & pull the actuator forward (away from the shaft).
3. Gently slide the actuator towards the shaft/lever until the shaft/lever stops moving, indicating the throttle-plate is seated.
4. Push the actuator another 2.0-2.5mm to "preload" the plate.
   • Too much preload may lead to the plate sticking after some time as the arrestor wears, & may also sacrifice full movement.
   
   
5. Tighten the fasteners, taking note not to allow the actuator to move.
6. Adjust the arresting/adjustment screw until it touches the lever, plus 1/4 to 3/4 of one turn.
   • Ideally, less clearance is better but too little and it will stick during thermal changes. Too much, & boost will bleed.
   
   
7. Manually rotate the lever to ensure the movement is smooth and unhindered during the action.
   • Do not pull on the actuator shaft itself as it is easy to tear the diaphram by moving it off the centreline.
   
   
8. Start the engine and note the movement, ensuring there is no "stiction".

Other items to check for include:

• A small amount of lubricant/grease on the lever/actuator interface.
• All hoses, tubes, elbows are fully engaged and not perished.
• The action of the lever is not interferred with from foreign articles (cable ties, NO2 plumbing, wires etc).

Hope this helps.

[unstable vic]

Ok this is getting confusing. I understand how it works. Do we do it or not?

[JamesZL1]

I am already making 15 lbs. right now..I think I will leave mine alone...lol

[hairtrigger]

Here is the key line...

Ideally, less clearance is better but too little and it will stick during thermal changes. Too much, & boost will bleed.

[97ChameleonTA]

Originally Posted by GenF-GTS

So there is no such thing as more air passing through the charger under normal driving conditions it will be open during non boost driving and air will divert over the charger instead of through it....then when under boost the vacuum will close the blade and it will boost up, if you have made the minor adjustment you will not lose any boost pressure leaking back out of the blade.

If the blade binds it can stick closed. This has happened to a few in the CTS-V crowd. When that happens the only path for the air is through the rotors. This causes excess IAT temps. That is the point of the preload. Not saying it needs 2 - 2.5mm preload but having the screw contacting the stop isn't a bad thing.

[oldfriend]

Originally Posted by jayno20

This is what I was thinking. I would adjust it so that screw is just BARELY not touching that way it still functions properly.

And would you take in consideration the metal expanding during normal engine operation ?
When one measure things up the engine is cold , but after the engine is running a few minutes it will heat up , and that space will close , or even push up against the contact

[KaBoom1701]

Originally Posted by oldfriend

And would you take in consideration the metal expanding during normal engine operation ?
When one measure things up the engine is cold , but after the engine is running a few minutes it will heat up , and that space will close , or even push up against the contact

+1

[1ZL4FUN]

Well I finally got 1500 miles on mine and did some WOT blasts and the car seemed a bit slower than I thought it should be. So I decided to do this mod. Mine moved a lot. More than 5 degrees and probably more like 10. This is in no way scientific but according to my seat of the pants (SOTP) AKA butt dyno, the car felt stronger. It also seemed to have a stronger/louder exhaust note at WOT. My comparisons are on different days and possibly different environment variables but I'd have to say I'm glad I did this. I don't have a boost gauge other than the stocker but the needle does seem to go a bit higher now. Keep in mind its hard to look at the gauge while at WOT LOL!!

On a side note I also decided to leave the engine cover off unless someone give me a good reason to put it back on other than looks. It seems to help the engine retain heat so it's going to stay on the shelf for a while.

[djnice]

Originally Posted by DrkPhx

GenF-GTS explained the bypass operation correctly. It's really simple. It's only fully closed at two different times; engine completely off and WOT. Closed = no boost bypass. At idle and part throttle the bypass is open to allow boost bleed off during normal engine operation. It should be adjusted anytime the snout is removed.

Are you sure we only get boost at WOT? Well, anyway that must also be why they integrated the no lift shift. So the diaphragm keeps the blade closed and it doesn't loose boost for a couple seconds during the shift.

[jayno20]

Originally Posted by oldfriend

And would you take in consideration the metal expanding during normal engine operation ?
When one measure things up the engine is cold , but after the engine is running a few minutes it will heat up , and that space will close , or even push up against the contact

Who said this would be done with the engine cold?